In almost all of the passenger type buses, exemplified by school buses, the seats are fixedly attached so as to be almost entirely immovable to the floor of the bus body with the result that once the seats are installed, they will stay in that one position until the bus body is entirely worn out.
In a few large vehicles for carrying a large number of passengers, the seats are arranged so that they can be detached from the floor of the body and either rearranged or entirely removed. Difficulties have been encountered with such seats, especially those which are fairly easily removable, because the seats, when installed, are simply not held firmly to the vehicle body but constantly wiggle and move around so as to be a source of noise and irritation to the passengers. Of course, such seats which are not tightly anchored can be dangerous because they may very well inadvertently release from their mountings so that, in the event of a sudden change of speed or direction, the seats may act like a missile to the injury of certain passengers.